Bacterial chemotaxis provides the opportunity to study sensory reception and motor function in a relatively simple system. Observation of motor function in bacteria is difficult because the small diameter of flagella (14 nm) does not provide much light scattering intensity in the microscope. By use of a carefully optimized optical system, it is planned to visualize individual flagella as well as the flagellar bundle. Further intensification of the image should be possible by the following means: Univalent antibodies attach to flagella without causing paralysis by cross-linking. Photomicrography (including cine) should then be possible with these artificially thickened flagella. Wild type and mutants defective in motility (e.g., paralyzed and polyhook mutants) will be studied. Intermittent tumbling is a characteristic of bacterial motility, and modulation of this tumbling as a result of chemical gradient-sensing is the means by which taxis is accomplished. The spontaneous tumble can be simulated by use of a high intensity pulse of blue light. This will provide a useful tool for examining the tumble, but the phenomenon is also of interest per se, particularly since specific interaction with chemotaxis has been demonstrated. Preliminary measurements of the action spectrum of the effect implicate a flavin; this spectrum will be refined and the effect of various metabolic inhibitors will be examined. Investigation of the gradient-sensing mechanism, which has been shown to involve a rudimentary "memory device", will be continued. Measurements of the time-scale of this memory should provide clues to the type of processes involved in retention of information about past environments.